The present invention relates to a method of detecting the reference crank angle position in an internal combustion engine at the time of starting the engine, and more particularly to a method of detecting the reference crank angle position, suitable for being carried out in an electronic engine control device such as an electronic ignition timing control device.
More and more internal combustion engines for use particularly on automobiles and motorcycles are equipped with electronic engine control devices such as electronic ignition timing control devices. Electronic engine control devices of certain types include a microprocessor (also known as a central processing unit which will hereinafter be referred to as a "CPU"). The CPU reads engine operation parameters such as the rotational speed of the engine, and controls the operation of the engine according to the engine operation parameters to achieve the best engine operating conditions at all times.
The CPU in the electronic engine control device is required to have information on the phase of the engine crankshaft, which is the relative angular position of the crankshaft during one cycle of engine operation with respect to a reference crank angle position that may be the angular position of the crankshaft when a certain piston is in the top dead center. The crankshaft phase information can be calculated from (1) information on the reference crank angle position which is obtained when the crankshaft reaches the reference angular position, and (2) information on the rotational speed of the crankshaft which is obtained by detecting the rotational speed of the crankshaft. One known means for producing such crankshaft phase information comprises a pulse generating mechanism including a toothed wheel of a magnetic material mounted on the engine crankshaft and an electromagnetic transducer or pickup for generating an electric pulse in response to detection of each tooth of the toothed wheel as it passes by he electromagnetic pickup. One example of a reference angular position detector employing such a pulse generating mechanism is disclosed in Japanese Utility Model Publication No. 58(1983)-26339. The disclosed reference angular position detector includes a rotor of a magnetic material attached to the crankshaft of an engine, the rotor having teeth disposed on its outer circumferential surface at angular intervals of an unit rotational angle .alpha..degree. for generating rotational angle information. The rotor also has one tooth-free recess for producing information on a reference crank angle position. The angular position detector also includes a pair of first and second electromagnetic pickups positioned adjacent to the rotor and angularly spaced along the outer circumferential surface of the rotor by a distance corresponding to a multiple of the unit rotational angle .alpha..degree.. As the engine rotates, the first and second electromagnetic pickups produce first and second pulse signals, respectively, which are subtracted one from the other to generate a differential output. The differential output is employed to detect when the second pulse signal from the second electromagnetic pickup is not generated at the tooth-free recess and only the first pulse signal from the first electromagnetic pickup is produced. The crank angle position at the time such a condition arises is detected as the reference crank angle position.
Immediately after the engine starts operating, the rotational speed of the engine is normally unstable or irregular, and the speed of movement of the teeth on the rotor past the electromagnetic pickups is low, so that the level of the pulse signals generated by the electromagnetic pickups is low. This has led to a drawback in that the second electromagnetic pickup may not produce a second pulse signal even when the tooth-free recess does not reach the position of the second electromagnetic pickup, thereby detecting the reference crank angle position in error. Consequently, whether a proper reference crank angle position is detected or not should be confirmed just after the engine has started to operate. For the automobile or motorcycle driver to get a smoother engine start-up, a proper reference crank angle position should be quickly confirmed and the engine should be operated under normal operation conditions in as short a period of time as possible immediately after the engine has started.